Eye Test - The Eye Chart and 20/20 Vision Explained On this page: What "20/20" means • Tumbling E eye chart • Jaeger eye chart • Limitations During an eye test, eye doctors use eye charts to measure how well you see in the distance, compared with other human beings. If you haven't established an eye doctor yet, click here to find one near you. The classic example of an eye chart is the Snellen eye chart, developed by Dutch eye doctor Hermann Snellen in the 1860s. There are many variations of the Snellen eye chart, but in general they show 11 rows of capital letters. The top row contains one letter (usually the "big E," but other letters can be used). The other rows contain letters that are progressively smaller. During an eye exam , your eye doctor will ask you to find the smallest line of text letters that you can make out, and ask you to read it. If you can read the bottom row of letters, your visual acuity is very good.

What 20/20 Vision In An Eye Test Means In the United States, the standard placement of the eye chart is on a wall that's 20 feet away from your eyes. Since many eye doctors' offices don't have rooms that are 20 feet long, in a smaller room the eye chart may hang behind the patient chair, using mirrors to make it appear in front of you at a simulated distance of 20 feet. How a Snellen eye chart and a "tumbling E" chart might look at your eye doctor's office. The tumbling E chart tests the visual acuity of young children and others who can't read letters aloud. [Read more about children's eye exams .] 20/20 vision (or really, 20/20 visual acuity ) is considered "normal" vision, meaning you can read at 20 feet a letter that most human beings should be able to read at 20 feet. Eye charts can be configured in various ways, but generally, if during an eye test you can read the big E at the top but none of the letters lower than that, your vision is considered 20/200.

That means you can read at 20 feet a letter that people with "normal" vision can read at 200 feet. So at 20/200, your visual acuity is very poor. Recommended For You Save 10-30% off your eye exam using the BenefitsPal™ card In the United States you are considered " legally blind " if your best-corrected visual acuity (meaning, your best distance vision with eyeglasses or contact lenses) is 20/200 or worse. To get a driver's license in most of the United States, your best-corrected visual acuity must be at least 20/40. Usually the 20/20 line of letters is fourth from the bottom, with 20/15, 20/10 and 20/5 below that. Not many people have 20/10 or better visual acuity, but many animals do, especially birds of prey, which have been estimated to have an acuity of 20/5 or even better. What is more important than your vision?

Find local eye doctor to get an eye exam "Tumbling E" Eye Chart In some cases a standard Snellen eye chart cannot be used. One example is when the person having the eye test is a young child who doesn't know the alphabet or is too shy to read letters aloud. Other examples include when the person is illiterate or has a handicap that makes it impossible for him to cognitively recognize letters or read them aloud. In these situations, a modification of the Snellen eye chart called a "tumbling E" chart may be used. The tumbling E chart has the same scale as a standard Snellen eye chart, but all characters on the chart are a capital letter "E," in different spatial orientations (rotated in increments of 90 degrees). The eye doctor asks the person being tested to use either hand (with their fingers extended) to show which direction the "fingers" of the E are pointing: right, left, up or down. Studies have shown that visual acuity measurements using a tumbling E chart are virtually the same as those obtained from testing with a standard Snellen eye chart. Download a Tumbling E eye chart and instructions for use here .

Near Visual Acuity: The Jaeger Eye Chart To evaluate your near vision, your eye doctor may use a small hand-held card called a Jaeger eye chart. The Jaeger chart consists of short blocks of text in various type sizes. A Jaeger eye chart contains several blocks of successively smaller text, generally ranging in size from J10 (large print) to J1 (very small print). The original Jaeger eye chart was developed in 1867 and contained seven paragraphs, each printed in a successively smaller font size. The smallest paragraph you could read when holding the chart approximately 14 inches away determined your near visual acuity. Since then, there have been several modifications of the Jaeger chart (or "Jaeger card") by different manufacturers. Unfortunately, modern Jaeger charts are not standardized, and the actual letter sizes on different Jaeger cards might vary slightly. The type scale on a modern Jaeger eye chart usually ranges from J10 (approximately 14-point type for Times New Roman font) to J1 (approximately 3-point type, Times New Roman). Some Jaeger charts have an additional paragraph labeled "J1+" that may be even smaller than the J1 block of text.

The J1 paragraph on a Jaeger card typically is considered the near vision equivalent of 20/20 visual acuity on a distance eye chart. On some Jaeger cards, the J1+ paragraph is the 20/20 equivalent. Common newsprint generally ranges in size between J7 (10-pt type) and J10 (14-pt type), which are the equivalent of 20/70 and 20/100 on a distance eye chart. A Jaeger eye chart may be used in two different ways, depending on what your eye doctor is trying to measure: The chart is held at a specified reading distance (such as 14 inches) and you are asked to read the passage with the smallest type you can see. The chart is moved forward and back until you are able to read a certain type size. Download a Jaeger near visual acuity chart and instructions for use here . Eye Chart Limitations Eye charts measure visual acuity only. They do help your eye doctor figure out whether you need prescription eyeglasses or contact lenses for your distance vision.

And they help the Department of Motor Vehicles to determine if you are required to use eyewear for driving, or if you shouldn't drive at all because you are legally blind. Watch this video on what causes blurry vision and how we can correct it. But eye charts don't measure your peripheral vision , depth perception, color perception or ability to perceive contrast . And they don't measure items related to the health of your eyes, such as your eye fluid pressure , whether you have glaucoma, how dry your eyes are or whether your retinas are in good shape. So eye chart testing is just one component of a complete eye exam , which you should have every one or two years. Home » Eye Exams » Eye Tests and the Eye Chart References & Notes >> Schwiegerling, J. Field Guide to Visual and Ophthalmic Optics. SPIE Press. 2004. Can Jaeger numbers be standardized. ARVO Annual Meeting abstract. Investigative Ophthalmology & Visual Science. May 2007. Khurana, AK. Theory and Practice of Optics and Refraction. Elsevier India. 2008. [Page updated November 2016] Like This Page? Please Share!

Recommended For You Eye Tests and the Letter Chart Media enquiries The inventor of the modern test chart was Dr Herman Snellen (1834-1908), a Dutch physician working in Utrecht. Before he set to work on the problem the patient was usually asked to read from a passage of text held in his or her hand, or held by the doctor or optician at a greater distance away. Snellen recognised that this was unsatisfactory, because there was no standardised size or design to the lettering that might be used. Passages using complicated vocabulary or sentence structure could also give a misleading result, or the patient could guess the next word from the context of the sentence. So in 1862 Snellen published his volume of ‘Optotypes’, which, for the first time, included characters that he thought were suitable for use on testing charts. It had single letters or numbers in addition to the more familiar reading tests. The patient had to name each character individually and letters that might be easy to confuse were deliberately placed near to each other on the chart. The same charts could be used at various distances, but there was no provision for standard illumination, which in any case would have been impossible in the 1860s.

Snellen’s work was translated into many languages within a few years of its introduction. Snellen’s Optotypes are not identical to the test letters used today. They were printed in an ‘Egyptian Paragon’ font and were of a serif style: that is they included ornamental cross strokes at the ends of each limb. Today you will normally have non-serif letters which are considered to be clearer. The first transparent test chart was devised in 1893 and was intended to be attached to the surface of a window in good daylight. It was reflected into a mirror to avoid glare. The first proper text chart with its own built-in light was designed in 1897. Lit by a gas light, it had a short working life as an instrument, because the light source bleached the chart and turned other parts of it yellow! In more recent years there has been a move to create electronic charts including the British-designed Test Chart 2000, which was the world’s first Windows-based computerised test chart. It overcame several difficult issues such as screen contrast, and offered the chance to change the letters often, so people don’t ‘learn’ them.

Eye Chart, Vision and Prescribing Eye Glasses | → Eye Doctor In Miami | Miami Optometrist | Clarin Eye Care Previous Next Mind Your P's and Q's – A Look At The Eye Chart For more than 100 years, Optometrists have used a typical eye chart in order to test your vision and find your most accurate prescription. To the patient, all eye charts must look about the same, but to me, there are vast differences. A brief history of the eye chart: the typical “ Snellen Chart ” is named after a Dutch Ophthalmologist who designed the chart in 1862 and is comprised of block letters. These letters have a standard and specific geometry, with each black line being the same thickness as each space within the letter, and the height being five times the size of each block. Originally, only the letters C, D, E, F, L, N, O, P, T, Z were used. These are the wall mounted charts that we see in all doctors offices, school nurse stations and and health clinics across America. Newer charts have a slightly different arrangement, and range from perfect block letters to fonts that even an eagle-eye couldn’t differentiate.

The whole idea of the eye chart is to make it confusing and difficult to discern if your vision is blurry, but crisp if you can see clearly. For instance, an F and a P look very similar if there is any slight blur. This is also true for a C or an O. Only the small openings at the far right differentiate these letters. It’s much easier to tell an A from a V even if your vision is a little blurry because of the letter form and the point facing either up or down. One curiosity to me as an eye doctor is how many people guess Q during the exam. The only difference between an O and a Q is the ‘descender’ (the downward vertical tail, I looked it up!). It’s actually funny to me that mostly adults guess Q– a child will never guess the letter. I figure that kids don’t expect such trickery during their exam and don’t over-analyze. In my exam room, I have three different letter configurations for each line vision. I still hear the same guesses and mistakes, and the same letters differentiate good vision with a particular lens versus blurry vision. The only advice I can give my patients is to never guess Q.

Connect with us: Snellen Chart | Your Eye Guide The Snellen Chart at an Eye Test Vision is usually measured using a Snellen Chart. This is composed of a series of black letters in rows, on a white board, and is typically used by optometrists. The chart is viewed at 6 metres. A visual acuity of 6/9 indicates that the chart was viewed at 6 metres and that the lowest line that could be read was labelled 9. Someone with normal vision would be able to read these letters at 9 metres. 6/60 vision indicates that someone could only see the top letter on the chart at 6 metres and that someone with normal vision would be able to read this letter at 60 metres. On most charts, the second from bottom line is 6/6. This is a normal good level of vision and what majority of people can expect to achieve. In the UK, driving standard falls between the 5th line (6/12) and the 6th line (6/9).

Test charts Test charts Print and Share Test charts Along with the trial frame, test letter charts are perhaps the objects most closely associated in the public's mind with the eye examination...but did you know that the idea of reading from a letter chart dates from as far back as 1862? Snellen's optotypes Herman Snellen (1834-1908) was a physician attached to the Netherlands Hospital for Eye Patients in Utrecht, a specialist eye hospital where he had worked for four years at the time of his ‘invention’. Various hospitals had already devised their own tests (using passages of readable text). These tests had multiplied in the wake of the invention of the ophthalmoscope in 1851, leading to a lack of standardisation. Snellen may have aimed to end this confusion as the result of a direct request from one of his mentors, the short-lived Albrecht Von Graefe (1828-1870). Whatever the reason, he is generally credited with being the first to introduce charts bearing single letters and numbers (optotypes, 1862) in addition to the more familiar reading tests.

The patient had to identify each alpha-numeric character individually and not just read complete words which might be guessed from the sense of the passage. He described these in an important work Optotypi ad Visum Determinandum which was quickly translated into French, German, Italian and English (Snellen was a noted Anglophile) and so became widely used internationally within a very short timeframe. The same charts might be used at various distances, but there was no provision for standard illumination, which in any case would have been impossible in the 1860s. They were available in an ‘English’ version from Williams and Norgate by 1864. Snellen's Optotypes are not identical to the test letters used today! They were printed in an 'Egyptian Paragon' font and were of a serif style: that is to say they included ornamental cross strokes at the ends of each limb. Ironically, the attempt in subsequent decades to ‘improve’ upon Snellen’s optotypes led to a re-divergence, whereby charts were no longer considered reliable as a comparable basis for estimating visual acuity (VA). This was particularly so of 1920s America.

Aside from discrediting the ophthalmic professions, this could have legal implications during hearings for compensation claims etc. Many charts were described as being ‘after Snellen’ without bearing much resemblance to his work at all (for example some Near Vision test types, in which area of work Snellen was never involved!) The history of ophthalmology... or of optometry? In 1877 Snellen was appointed Professor Ordinarius in ophthalmology at his old alma mater, the University of Utrecht. Other ophthalmologists were involved in designing new letter-types. These included John Green (1835-1913), Professor of Ophthalmology and Otology in the St Louis College of Physicians and Surgeons, Missouri from 1866. He took up that appointment shortly after returning from an extended stay in Europe, and the design of his test types in 1868 may be seen as one consequence of those travels. Green was the first to experiment with non-serif style letters (of a Gothic style), but this was a false dawn as, stung by criticism over their unfinished appearance, he favoured serif letters once again from 1872.

Ferdinand Monoyer (1836-1912), a specialist in physiological optics, ran an ophthalmic clinic at the hospital in Nancy, France. Monoyer is credited with introducing the first test-types corresponding to a decimal system in 1875. A year later he was appointed to a professorship of medical physics at the University of Lyon. Monoyer selected his font style on an individual letter by letter basis. He felt there was a case for not selecting the same linear dimensions in every instance. For example a letter H that is as wide as it is high can look too drawn out. Dennett (USA 1885), Blaskovics (Hungary 1923/4), Cowan (USA 1928) and Walker (Great Britain 1942) all produced varieties of test type that found favour at one time or another. This is probably mainly due to the fact that eye hospitals were the main source of research in this period, with training for ophthalmic opticians still being a combination of apprenticeships, evening classes and the odd technical college course.

Attempts at standardisation were the work of ophthalmological congresses (1872, 1904, 1909, 1922). For example the International Congress of Ophthalmology held at Naples in 1909 selected the numerical chart of Carl von Hess (1863-1923), Professor of Ophthalmology at the University of Wurzburg, as the international standard. Its 'Minimum separabile' was to be the minute of arc. In Great Britain, however, a separate optometry profession was growing from the 1890s onwards and the Institute of Ophthalmic Opticians (IOO) did much development work from the 1920s onwards, resulting in Harold Emsley’s IOO Chart of 1933. In more recent years there has been a move to create electronic charts. Test Chart 2000, designed by Dr David Thomson of the Department of Optometry at The City University, London, was launched in January 2000, and was the first Windows-based computerised test chart in the world.

It overcame several hitherto difficult issues such as screen contrast, and offered the chance to vary the letters shown on a frequent basis. In Britain there are now several university-based optometry departments, and only a minority of patients would have their eyes tested by an ophthalmologist (for whom refraction is an increasingly rare activity), but elsewhere in Europe opticians remain barred from performing refraction and so to them it would not seem strange to refer to Snellen’s chart as a contribution to the ‘history of ophthalmology’. It is fair to say that optometrists in Britain (and some British-influenced countries) and sight-testing ophthalmologists elsewhere are equally the heirs of Snellen. Reversed letter charts In the 1940s reversed test-types were filtering through to Great Britain from America, and seemed likely to become the new standard. The patient sat with the chart behind him and viewed the lines through a mirror which had the effect of doubling the distance at which the letters appeared. It was noted, however, that sometimes opticians were invited to refract in ophthalmic hospitals where they could find bigger facilities allowing for a direct chart to be placed at further than six metres from the patient. In 1947 L.A.

Swann reminded such practitioners that such facilities could be equally scientific, even if less convenient. This points to an interesting factor - that the development of test charts has partly been driven by the amount and nature of space available for consulting rooms. Astigmatic charts Astigmatic letters (made up of split vertical, horizontal or oblique lines) can be traced back to the American chart of Dr Pray (sometimes written Prey) in 1869. Many test chart cabinets incorporate 'Snellen's dial', a fan-like arrangement of lines, alongside the more conventional optotypes. Foreign language charts The first test charts were Dutch-inspired and so utilised western letter forms and so-called 'Arabic' numerals. As sight-testing spread to other countries, the Snellen type was adapted to fit local circumstances. Examples might include Gothic script, suitable for German-speaking areas, or charts in Hebrew. The motivating force behind the latter type of chart may have been the signficant number of opticians who were Jewish. In the East End of London many of their patients would have been unable to read any other language.

The Emarah Chart designed in 1968 was a pioneering Arabic language test letter chart on a panel of laminated perspex board intended for insertion into a test chart cabinet. That way an optometrist's equipment could be quickly adapted in the event of an influx of Arabic speakers into a local area. The chart was also supplied with two phonetic translation cards in classical Arabic for the benefit of the English-speaking optometrist. It was devised by a professor at the University of Cairo in collaboration with I.D.C Pain of Keeler Ltd. Though drawn from the Arabic alphabet, the letters conform to the Snellen principle of 1-unit line width and 1-unit interspace. (See British Journal of Ophthalmology, Vol 52 (1968) p.489-91). Naturally, some compromise was involved, and the particularly cursive form of the flowing Arabic letters had to be straightened to some extent. An inadvertent result was that to us, viewing the chart forty years on, it appears to contain a smiley face emoticon! Illiterate charts How do you ask a patient to identify the test objects if he cannot read or cannot count?

The Army made effective use of Snellen charts, but found that in practice some recruits could not read. They had to add in their own charts comprised of dots in a line such as that illustrated above to the right which dates from 1864. A chart employing arrangements of dots (not unlike dominoes) was used to test Prussian military recruits by the Army physician Max Burchhardt (1831-1897) as early as 1869. The Landolt ring is the classic illiterate test. The break in the ring (making it look like a letter 'C') can be turned in any direction and the patient asked to point it out. Similar in concept is the Illiterate 'E' which is really to be considered as a vertical line with three shorter lines stemming from it. Again, an ability to spot the direction in which these face can determine the acuity of the patient. These charts are often made portable, as they have traditionally been applied for domiciliary use. Illuminated charts Whilst the first transparent test chart was devised in 1893 by Cohn, it was intended for use attached to the surface of a window and required sufficient daylight.

Even then it was reflected into a mirror due to the need to avoid glare. The first proper text chart with it own integral illumination was designed by Roth in 1897. Lit by a gas light, it had a short working life as an instrument because the light source bleached the chart and turned other parts of it yellow! Charts could either be internally or externally illuminated. Ultimately the internally illuminated design won out. It looked neater and was more practical, for example, when a chart was desgined to revolve. Projection charts Another space-saving solution was to project a slide of the test letters onto a viewing surface such as a white wall. The oldest patent for such a device appears to be American, dating from 1922. Before the War the Fleming Project-O-Chart was heavily advertised though it is unclear how many were ever actually sold. You had to order either the 'A' or the 'B' lens system depending upon whether you intended to project over distances of more than fifteen feet.

The Ferree-Rand projector by Bausch & Lomb, produced during the Second World War, was commercially successful, to a limited degree, outside the States, though like many ophthalmic instruments the extent to which it penetrated the British market was restricted due to high import tariffs. Our museum's example was imported by Frank Dickinson FBOA. It has a rectangular base, tapering tube and a semi-circular lamp unit. An adjustable diaphragm sits at the narrow end of the tube. The charts are inserted to the wider end as transparent slides. They include a vertical red and green "Chromatest" slide and a horizontal slide bearing test letters and astigmatism diagrams. Other test chart instruments The Visometer (unfortunately one of several optical instruments, designed for different purposes, to bear that name) was invented in 1913 by Kirsch. A reduced size test letter target was viewed through lenses as it moved along a scale to replicate the placing of larger letters at a distance. S.R. Stearman designed a version which was described in the Optician (24.2.1933, p.30).

The J & R Fleming catalogue for 1936 states that the instrument is 'the result of extensive research into the construction of subjective test charts. The test letters have been carefully selected and grouped to reduce errors due to guessing'. Did you know? Test letter charts are classed as a 'subjective' test. That is because their use requires some input from the patient, whose response might be offered as a matter of opinion. e.g. a question 'What is the last line you can read clearly?' may not have a definitive answer. A full eye examination should therefore contain a good balance of subjective and objective tests. Some useful sources for historians of test letters: Anon, 1922, ‘The Invention of Test Types’, The Optician and Scientific Instrument Maker, (28 July 1922) p.370. Anon, 1962, ‘A Snellen Centenary’, The Optician, (28 September 1962) p.298.

Bennett, A.G., 1965, ‘Ophthalmic Test Types - A Review of Previous Work and Discussions on Some Controversial Questions’, British Journal of Physiological Optics, 22 (4), p.238-271. Coates, W.R., 1935, ‘Visual Acuity and Test Letters’, The Optician, (20 and 27 September 1935), pp.90-92, 108-109. [Substance of paper delivered by Coates to Institute of Ophthalmic Opticians, 12 September 1935]. Jackson, A.J. and Bailey, I.L., 2004, 'Visual Acuity', Optometry in Practice Vol 5 (2004) p.53-70. Swann, L.A., 1947, ‘Direct or Reversed Test Types?’ The Optician, (7 February 1947), p.3-4.

Tonkelaar, I, Henkes, H and van Leersum G, 1996, Eye and Instruments, Nineteenth Century Ophthalmological Instruments in the Netherlands, Batavian Lion, Amsterdam. All these titles are available in the College Library . Reading A Letter Chart - Look After Your Eyes Reading a letter chart Can I take my prescription elsewhere? Reading letters on a chart is one of the most familiar parts of an eye examination. You are asked to read whichever line of letters you can see clearly. That helps the optometrist find out how well you see, and also – if you need glasses – how they will work best for you. The chart may be hanging on the wall opposite where you sit, or it may be behind you so that you look at its reflection in a mirror. It may be a fixed chart or it may change to vary the letters shown. It may be on a computer screen or on a screen where the letters are illuminated. You may also come across charts which use only one letter presented in multiple directions, usually a C, an E or an F. The standard distance between the patient and the chart is six metres, or 20 feet.

However, if space is limited, your optometrist can create that distance by reflecting the letters in a mirror. fonts, typefaces and all things typographical — I love Typography (ILT) MADE POSSIBLE WITH THE SUPPORT OF My graphic design students love to design posters using the classic eye chart composition, and they frequently ask “What typeface should I use for this?” Not having a definitive answer has always been frustrating, so I decided to investigate to find out what typeface is used on eye charts. July 12, 2015 Lorrie Frear I started my quest by asking my ophthalmologist, who enthusiastically provided a dizzying amount of technical information about the variety of eye charts and tests designed for different audiences and eye conditions. Suddenly, a simple question became a series of discoveries. Not only is there not one letterform design or font used for eye charts; the letterform designs are more appropriately called optotypes, of which there are several versions. There is a science to the design of optotypes and their legibility at specific distances.

Since I am a graphic designer and not an eye or vision expert, I will forgo the technical explanations and focus on optotypes used on several significant charts to provide a better understanding of this complex and fascinating subject. Eye charts are designed to test visual acuity, or clarity of vision. Each chart design has limitations and advantages, depending on the clinical setting, patient profile, and diagnostic objective. To understand the differences between the charts, it is helpful to know a little historical background of standardized visual acuity testing. The First Standardized Tests Figure 1: Kuchler Chart. Heinrich Küchler is one of the first individuals credited with creating an eye chart to test visual acuity. Küchler, a German ophthalmologist, designed a chart in 1836 using figures cut from calendars, books, and newspapers glued in rows of decreasing sizes onto paper. These figures included cannons, guns, birds, farm equipment, camels, and frogs. This system was limited because the figures were not consistent in visual weight or style. Dr. Küchler continued to refine his chart, and in 1843, published a new version using 12 rows of Blackletter letters decreasing in size.

This chart was not widely adopted (hard to imagine why) and was published only once in 1843. 1 Figure 2. Snellen Chart The next significant development in visual acuity chart design was the Snellen Eye Chart, which is recognizable to most Americans from visits to the DMV. The Snellen Eye Chart was designed by Dutch ophthalmologist Herman Snellen in 1862 as a means to improve the subjective nature of vision testing, which was usually accomplished by having patients read a passage of text held their hands, or held at a distance by the doctor. This test had obvious limitations: the results were dependent upon the reading ability of the patient, the legibility of the typeface used, and the fact that the patient could guess the next word by reading a sentence. According to Dr. August Colenbrander, a scientist at the Smith-Ketterwell Eye Research Institute and an expert on eye chart design, Snellen began experimenting with dingbats, or symbols such as squares and circles for his eye chart, but found that it was difficult for test subjects to describe the symbols accurately. 2 So, he moved on to using letters.

The characters on the first Snellen Charts were: A, C, E, G, L, N, P, R, T, 5, V, Z, B, D, 4, F, H, K, O, S, 3, U, Y, A, C, E, G and L. The letters used were Egyptian Paragons or slab serifs of contrasting line thickness with ornamental cross strokes on terminals. Snellen then theorized that test subjects would be able to identify non-ornamented, monoline/equally weighted letters of consistent visual size more easily, and so he created optotypes. 3 Figure 3. Snellen vs Lubalin Graph At first glance, it may appear that the Snellen optotypes are Lubalin Graph or Rockwell. But upon detailed examination, it is evident that these characters are rather atypical. Unlike typical typefaces in which letter proportions are determined by ‘family’ groupings (such as n, r, m, h and u), Snellen optotypes are designed on a 5 x 5 grid. Furthermore, they comprise a very limited character-set of just 9-10 letters.

Optotypes are designed using a simple geometry in which the weight of the lines is equal to the negative space between lines. The height and width of an optotype is five times the thickness of the line weight. 4 These design considerations create inconsistently and oddly proportioned letters. For example, in a typical typeface, C and D would appear wider than Z, but in the optotype scheme, the opposite is true. Figure 4. Snellen letter E Dr. Snellen created Optotypes using minutes of arc instead of a typographic measuring system. This made it possible for his charts to be reproduced easily. The first large order for Snellen Charts was from the British Army in 1863. From there, the Snellen Eye Chart became the standard for vision testing for almost a century. In addition, Snellen’s 5 x 5 grid optotype design is the foundation upon which all other eye chart systems are based. The Snellen Eye Chart is still the most recognized design, which can, to some extent, negate its effectiveness, if, for example, the test subject has memorized the chart. 5 Most Snellen Charts contain eleven lines of block letters. The first line consists of a single large letter, most often an E.

Subsequent rows have increasing numbers of letters that are progressively smaller in size. The test subject, from a distance of 20 ft, covers one eye, and, beginning at the top, reads aloud the letters in each row. The smallest row that can be read accurately indicates the visual acuity in that particular eye. 6 Current Snellen Charts use nine letters, C, D, E, F, L, O, P, T, Z. Note that with the exception of E and O, the letters are all consonants. The diverse shapes of the optoypes allow test subjects to identify verticals, horizontals, and diagonals. These letter shapes are also highly effective in identifying astigmatism. Although today’s Snellen Eye Charts may vary in the number of rows, size gradation, and serif or sans serif design, 7 their commonalities include the rectangular shape. This dictates the varying numbers of optotypes appearing on each line as space permits. 8 As a result of continual refinements, most of today’s Snellen Charts follow logarithmic progression, have improved letter designs, and a uniform 25% progression from line to line. 9 Refinements and Variations In 1868, Dr.

John Green of the St. Louis College of Physicians and Surgeons in Missouri decided to make some changes to the Snellen Eye Chart. He designed a more structured grid featuring a consistent logarithmic geometric progression of 25% for successive lines, and with proportional spacing. He also changed the style of the optotypes from the blocky slab serif to sans serif. His concept became known as the “Preferred Numbers Series,” but his system did not become widely recognized until the next century when sans serif typography gained popularity. Ironically, in response to criticism that his letters looked “unfinished”, Dr. Green abandoned them in 1872, and returned to the serif optotypes. 10 Figure 5. Sloan Chart In 1959, Dr. Louise Sloan of Johns Hopkins University created ten new optotypes using sans serif letters preferred by Dr. Green. These optotypes included the letters: C, D, H, K, N, O, R, S, V, and Z. Like Snellen letters, Sloan Letters are formed within a square, with the stroke width equal to one-fifth of the letter height and with equal visual weight. The Sloan Chart has consistent spacing between letters and rows that are proportional to letter size.

Spacing between letters is equal to letter width, and spacing between rows is equal to the height of the letters in the subsequent, smaller row. 11 Notice that, as in the Snellen Chart, all of the characters are consonants with the exception of 0. Also note that the letter selection used on the Snellen Chart is not the same as that in the Sloan Chart. In both cases, the diverse shapes of the optoypes allow test subjects to identify verticals, horizontals and diagonals – an aid to identify or differentiating individual letters. The ten Sloan Letters are considered to be the most effective letter selection for equal legibility. What’s more, they are particularly effective at identifying astigmatism. Figure 6 The Sloan Letters may at first glance resemble Microgramma or Eurostile fonts , but upon closer examination, it is evident again that the grid format imposed upon these optotypes produces some odd and inconsistently proportioned letters.

New Charts and Methods Figure 7 In 1976, Ian Bailey and Jan E Lovie-Kitchin of the National Vision Institute of Australia proposed a new chart layout, describing their concept as follows: “We have designed a series of near vision charts in which the typeface, size progression, size range, number of words per row and spacings were chosen in an endeavor to achieve a standardization of the test task.” 12 This layout replaces the Snellen rectangular chart format with a variable number of letters per line with a triangular one with five proportionally spaced letters on each line. The ten Sloan Optotypes appear on the Bailey-Lovie Chart using the same letter ratio of the letter-height equal to five stroke widths, excluding serifs. Figure 8. The Bailey-Lovie Chart is an example of a LogMAR test, a term describing the geometric notation used to express visual acuity. “Logarithm of the Minimum Angle of Resolution” or (LogMAR) tests, were selected, in 1984, as the standard for visual acuity testing by the International Council of Ophthalmology.

13 In 1982, when the National Eye Institute needed standardized charts for its “Early Treatment of Diabetic Retinopathy Study” (ETDRS), Dr. Rick Ferris combined the Green and Bailey-Lovie Charts’ logarithmic progression and format with the Sloan Letters. ETDRS charts use equal spacing between letters and lines, making the acuity chart more balanced. 14 This chart format has been accepted by the National Eye Institute and the FDA, and is mandated for many clinical trials performed worldwide. The ETDRS test is more accurate than either the Snellen or Sloan versions because the rows contain the same number of letters, the rows and letters are equally spaced on a log scale, and individual rows are balanced for letter difficulty. There are also three different versions of the test available to deter memorization. 15 One limitation of the original ETDRS chart is its use of the Latin alphabet, making it difficult to use throughout all of Europe. To address this limitation, the Tumbling E and Landolt C charts are used for populations who are unfamiliar with letters of the Latin alphabet. Recently, a modified ETDRS chart was developed using Latin, Greek, and Cyrillic alphabets.

For this chart, the standard letters C, D, N, R, S, V and Z have been replaced by the letters E, P, X, B, T, M, and A. These letters are created using the same 5 x 5 grid and the Sloan Letters. 16 Figure 9. Tumbling E Chart In more recent years there has been a move to create electronic charts, including the British-designed Test Chart 2000, which was the world’s first Windows-based computerized test chart. It overcomes several difficult issues such as screen contrast, and provides the opportunity to change the letter sequence, so that it cannot be memorized. 17 These fonts, for Mac and Windows OSs, are available for research purposes. The fonts are based on Louise Sloan’s designs, which has been designated the US standard for acuity testing by the National Academy of Sciences, National Research Council, Committee on Vision. 18 Charts for Non-Readers For testing patients who cannot read or for those unfamiliar with the Latin alphabet, the Tumbling E Eye Chart and the Landolt C or Broken Ring Chart are used.

19 The Tumbling E Chart was designed by Professor Hugh Taylor of the Centre for Eye Research Australia (CERA) in 1978 to test the vision of Australian Aborigine individuals in an attempt to identify those with the eye disorder, Trachoma. Professor Taylor, using the Snellen proportions, designed a shape resembling an uppercase E, which he arranged in four directions (up, down, right, and left) in progressively smaller sizes. The patient then simply describes the direction in which the Tumbling E is facing. Figure 10. Snellen E and Tumbling E Figure 11. Landolt C Chart The Landolt C or Broken Ring Eye Chart is also used for illiterate individuals or those persons unfamiliar with the Latin alphabet. Created by Swiss ophthalmologist Edmund Landolt, this test is now considered the European standard. The Broken Ring (which is the same proportions as the C from the Snellen and Sloan Charts) is rotated by increments of 90°. The minimum perceivable angle of the C-gap is the measurement of visual acuity. 20 In addition to the Tumbling E and Landolt C tests, there are charts for children in which progressively smaller, simple pictograms of objects are used.

The challenge in designing these charts is creating recognizable pictograms of equal visual weight, consistent style, and design. Figure 12. Snellen C and Broken Ring Eye Chart C This article is not an exhaustive research study into the subject of eye charts or their efficacy. There are many more examples of eye charts. My objective was to explore the archetypes of optotype design in the evolution of the eye chart as a diagnostic tool. Now I can tell my students that there is, technically, not a single typeface to recommend for their designs; and I can refer them to this article for more information! Examining optotypes has been an eye-opening experience. Footnotes: Vision tests - Essilor Group Vision tests FROM A VISION TEST TO EYE EXAMINATION What is the difference between vision tests and an eye examination? What are their benefice and which one choose? Find out all the answers to your questions. TEST YOUR VISION Do you sometimes screw up your eyes to read signs properly? Does your vision go fuzzy when you read? Do you have difficulties driving at night? Why not start by testing your vision online. It’s quick and simple. Fingers at the ready? Let’s get testing…

Question: What letter is at the top of an optometrist's eye chart?
Answer: E